The long range goal of this project is to examine, by electron microscopy, cells from tissues of mice, rats, monkeys and humans of various ages, to determine what similarities and differences exist, in terms of age related, structural changes, between different cell types of individual species and between similar cell types of the different species. Comparisons are being made between in-vivo models and in-vitro models at both the transmission and scanning electron microscopic levels. The effects of diet, stress, and drugs on the rate of aging at the cellular structural level are being examined.